The present invention relates in general to an automatic saw cutting machine for cutting tubes in double-tube cutting mode, and more specifically to a roller feed unit for such a machine.
In the description and claims which follow, the term “tube” is used to designate any elongated body having a uniform cross-section along its longitudinal axis, the cross-section being either open or closed. Moreover, the terms “longitudinal” and “transverse” are used to designate the forward direction (or feed direction) of the tubes and any direction lying in a plane perpendicular to the longitudinal direction, respectively.
As is known, a machine of the above-identified type basically comprises a loading unit for loading the tubes to be cut, a roller feed unit for feeding the tubes to the cutting area, a chuck for clamping the tubes during the cutting operation and a cutting head provided with a circular saw for cutting the tubes. The machines currently available on the market can be classified in two main categories: 1) machines arranged to carry out the cutting process in the so called single-tube cutting mode, i.e. to cut one tube at a time; and 2) machines arranged to carry out the cutting process in the so called double-tube cutting mode, i.e. to cut two tubes at a time. The configuration and the operation of the loading unit and of the feed unit of a machine vary in particular depending on the cutting mode that is used in that machine.
The loading unit typically comprises a tube collecting area, a conveying device and a selecting device. The tubes to be cut are collected in the collecting area, with their longitudinal axes parallel to each other, and are moved laterally from that area by means of the conveying device, which comprises for example a set of chains, to the selecting device, in which the tubes are selected two by two.
The feed unit receives the two tubes from the loading unit and feed them to the cutting area, where the two tubes are clamped by the chuck and then cut to size by the circular saw of the cutting head. In the saw cutting machines with roller feed unit, like that of the present invention, the cut length of the two tubes is defined by a respective abutment member against which the tube to be cut is urged until abutment.
FIGS. 1 and 2 of the attached drawings schematically show a transverse section view (i.e. a section view through a section plane perpendicular to the longitudinal axis of the tubes to be cut) and a side view, respectively, of a known example of a roller feed unit for a saw cutting machine for cutting tubes in double-tube cutting mode. With reference to FIGS. 1 and 2, the feed unit is generally indicated 10 and comprises first of all a first pair of lower rollers 12a, 12b, that is to say, an upstream lower roller and a downstream lower roller (wherein the terms “upstream” and “downstream” are referred to the forward direction of the tubes, indicated by arrow F), respectively, that are associated to a first tube feed line (left-hand line, with respect to the point of view of a person looking at FIG. 1), the axis of which is indicated x1, and a second pair of lower rollers 14a, 14b, that is to say, an upstream lower roller and a downstream lower roller, respectively, that are associated to a second tube feed line (right-hand line, with respect to the point of view of a person looking at FIG. 1), the axis of which is indicated x2. The upstream lower rollers 12a, 14a are rotatably mounted about the same transverse axis of rotation ya, in particular a horizontal axis of rotation. Likewise, the downstream lower rollers 12b, 14b are rotatably mounted about the same transverse axis of rotation yb, in particular a horizontal axis of rotation, hence parallel to the axis of rotation ya of the upstream lower rollers. The lower rollers 12a, 12b, 14a, 14b are all motor-driven rollers and therefore will also be referred to hereinafter as driving rollers.
The feed unit 10 of FIGS. 1 and 2 further comprises a first pair of upper rollers 16a, 16b, that is to say, an upstream upper roller and a downstream upper roller, respectively, that are associated to the first tube feed line (axis x1), and a second pair of upper rollers 18a, 18b, that is to say, an upstream upper roller and a downstream upper roller, respectively, that are associated to the second tube feed line (axis x2). Like the lower rollers, the upstream upper rollers 16a, 18a are rotatably mounted about the same transverse axis of rotation y′a, in particular a horizontal axis of rotation, and the downstream upper rollers 16b, 18b are also rotatably mounted about the same transverse axis of rotation y′b, in particular a horizontal axis of rotation, which is therefore parallel to the axis of rotation y′a of the upstream upper rollers. The upper rollers 16a, 16b, 18a, 18b may either be idly mounted about the respective axes of rotation or be motor-driven. Moreover, the upper rollers 16a, 16b, 18a, 18b are vertically movable, for example by means of a rocking support 20, to be urged each towards a respective lower roller 12a, 12b, 14a, 14b with a given preload (that can be adjusted for each upper roller independently of the other rollers), in order to ensure that each tube (indicated T1 for the first feed line and T2 for the second feed line) is clamped with a given clamping force between a lower roller and an upper roller. Therefore, the upper rollers will also be referred to hereinafter as pressing rollers.
The feed unit 10 of FIGS. 1 and 2 further comprises side retaining rollers, that are idly mounted about respective vertical axes of rotation, namely a series of first side rollers 22 (only shown in FIG. 1) adapted to retain laterally the tube(s) along the first feed line (axis x1), a series of second side rollers 24 (only shown in FIG. 1) adapted to retain laterally the tube(s) along the second feed line (axis x2) and a series of intermediate rollers 26 that are interposed between the two lines of tubes T1 and T2 that are fed to the cutting area.
In a known feed unit for an automatic saw cutting machine for cutting tubes in double-tube cutting mode, like the one described above with reference to FIGS. 1 and 2, the two feed lines are plainly distinct from each other, since the tubes on the two feed lines are always kept at a distance from each other by means of the intermediate rollers.